The invention relates to a restraining system for occupants of a motor vehicle, with an inflatable airbag which is assigned to the occupant in combination with a safety belt and which, in the event of an accident to the motor vehicle, is automatically inflated by means of a gas generator with pressure controllable in dependence on the fastening state of the belt.
A corresponding restraining system is known from German Published Application No. 4,032,757. Here, inflation pressure of an airbag serving as an impact-protection cushion for a motor-vehicle occupant is controlled in dependence on the fastening state of a safety belt by means of two separately activatable gas generators.
It is known from German Patent Specification 3,413,768 to make the gas generator of an airbag two-stage, in the event of an accident the first stage being ignited at a relatively low impact speed of the vehicle, whilst the ignition of the second stage takes place only at a higher impact speed. In this way, the airbag is inflated comparatively weakly at a lower impact speed and to a greater extent at a higher impact speed.
A further restraining system with an airbag is known from German Published Application No. 3,702,825, and in this, in the event of an accident, the gas generator of the airbag is already ignited at a relatively low impact speed, if the particular occupant has not fastened the safety belt. In contrast, with the belt fastened, the ignition of the gas generator takes place only at an increased impact speed.
It is known from German Patent Specification 2,120,043 to maintain the gas generator at a substantially constant operating temperature by means of heating, so that the inflation pressure of the airbag has a value which can be reproduced with particular accuracy.
An object of the invention is, in a restraining system of the type mentioned in the introduction, to guarantee in an especially simple way in terms of construction that, in the event of an accident, the airbag is inflated differently, depending on whether the particular occupant has fastened the safety belt or not.
This object is achieved according to the invention in that the gas generator possesses a heater which switches on only when the belt is not fastened.
The invention is based on the generally known fact that the airbag should be inflated with reduced pressure only when the particular occupant has fastened the safety belt, in order as far as possible to avoid the risk of minor facial injuries which can occur when the occupants head strikes the airbag. On the other hand, it is necessary to guarantee that the airbag is inflated with increased pressure if the occupant has not fastened the belt; for in this case, sufficient safety of the occupant can be guaranteed only by means of increased pressure and possible minor facial injuries must be allowed for.
In order to guarantee the mode of operation of the airbag or gas generator which differs according to the use of the belt, the invention makes use of the fact that the inflation pressure of the airbag clearly depends on the temperature of the gas generator. Now according to the invention, this effect, which has been disturbing in previous airbag systems, is utilized for controlling the inflation pressure, by providing for a heater which remains switched off when the belt is fastened and is switched on when the belt is not fastened, so that a reduced inflation pressure is guaranteed in the first instance and an increased inflation pressure in the second instance.
In an embodiment which is expedient in terms of construction, the safety belt has a belt buckle which is coupled to a switch which then itself switches on the heater when the belt is not locked in the belt buckle and switches off the heater when the belt is locked in the belt buckle.
The switch is expediently arranged in series with an operating switch of the vehicle engine, so that the heater can be switched on by the switch only when the vehicle engine is running.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.